A basic doctrine of reproductive biology, which states that mammalian females lose the capacity for germ-cell renewal during fetal life, has only recently been successfully challenged by Johnson et al., (2004) Nature 428: 145. Johnson et al. are the first to conclusively demonstrate that juvenile and adult mouse ovaries possess mitotically active germ cells that, based on rates of oocyte degeneration and clearance, sustain oocyte and follicle production in the postnatal mammalian ovary.
It has been recently determined that the precursors of germ cells are not confined exclusively to the ovaries. Germ cell marker genes have now been identified in cells derived from bone marrow. In addition, transplantation of bone marrow to a conditioned host allowed for bone marrow cell development into new oocytes within the ovary.
Umbilical cord blood from newborn infants is a known reservoir of stem cells that may contribute to a variety of somatic cell lineages, including hematopoietic precursors (for reviews see Korbling and Anderlini 2001 Blood 98: 2900-2908; Ho and Punzel, 2003 J Leukoc Biol 73: 547-555; Sanchez-Ramos 2002 J Neurosci Res 69: 880-893; Lee 2004 Blood 103:1669-75). Cord blood samples are easily and safely collected and may be stored for future therapeutic use (Rogers and Casper 2004 Sexuality, Reproduction & Menopause 2: 64-70); further, their availability to individual patients offers a potential source of perfectly-matched donor cells. It was heretofore unknown whether peripheral blood, such as cord blood also contained germ cell precursors.